Introduction
Electrostatic coalescers are used for crude oil dehydration in both Production and Refining. These devices enhance the coalescence of water droplets by the use of an applied electric field. In a strong electric field, water droplets have an induced dipole and are deformed into an ellipsoidal shape. Attraction between the positive and negative ends of adjacent water droplets is a driving force for coalescence. Distortion of the stabilizing emulsifier film (solids, surfactants, asphaltenes, and other compounds) surrounding the water droplets also assists in droplet coalescence.
Chemical additives, such as demulsifiers and solids-wetting agents, are often used in conjunction with applied electric fields for crude oil dehydration. These additives function to destabilize the emulsifier film surrounding the water droplets. Portable batch electrostatic coalescers are used by chemical vendors to conduct quick screening tests for selecting the best chemical additive package for a given crude oil/brine system. These experiments rank order the relative performance of different additive packages and approximate their performance in commercial-scale electrostatic coalescers.